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Feature-Oriented Programming with Object Algebras

Object algebras are a new programming technique that enables a simple solution to basic extensibility and modularity issues in programming languages. While object algebras excel at deï¬ning modular features, the composition mechanisms for object algebras (and features) are still cumbersome and limited in expressiveness. In this paper we leverage two well-studied type system features, intersection types and type-constructor polymorphism, to provide object algebras with expressive and practical composition mechanisms. Intersection types are used for deï¬ning expressive run-time composition operators (combinators) that produce objects with multiple (feature) interfaces. Type-constructor polymorphism enables generic interfaces for the various object algebra combinators. Such generic interfaces can be used as a type-safe front end for a generic implementation of the combinators based on reï¬‚ection. Additionally, we also provide a modular mechanism to allow diï¬€erent forms of self-references in the presence of delegation-based combinators. The result is an expressive, type-safe, dynamic, delegation-based composition technique for object algebras, implemented in Scala, which eï¬€ectively enables a form of Feature-Oriented Programming using object algebras.

A follow-up to Object Algebras, this new paper addresses a few of the limitations described in that LtU thread by adding type constructor polymorphism to increase their safety. The paper describes an implementation in Scala, which is the only widely available statically typed OOP language with a sufficiently powerful type system needed to support FOP.

This new work also describes some composition mechanisms for object algebras in the context of more expressive languages.